HIV-1 integrase (IN) is essential for viral replication and thus is an important therapeutic target. During the early stages of viral replication, a tetramer of HIV-1 IN catalyzes integration of reverse transcribed viral DNA into the host genome. The ordered multimerization of IN in the presence of viral DNA is critical for IN catalytic activity. Cellular cofactor LEDGF/p75 binds to the pre-assembled IN- viral DNA complex and tethers the nucleoprotein complex to active genes, thus ensuring effective integration. Allosteric integrase inhibitors (ALLINIs) are a novel class of integrase inhibitors that bind at the LEDGF/p75 binding site at the IN dimer interface and are capable of triggering aberrant IN multimerization. In addition, HIV-1 virions produced in the presence of ALLINIs display abnormal morphology of the virion cores and are defective for subsequent reverse transcription and integration in target cells. Interestingly, these phenotypes are similar to certain IN mutants, which have been termed class II mutants. Collectively, the studies with ALLINIs and select IN class II mutants suggest that HIV-1 IN plays a key role during late stage HIV-1 replication. However, the underlying mechanism is not clear. The present application will test the following hypothesis: ordered IN multimerization is important for its interaction with viral RNA during the late stage viral replication. Therefore, we propose the following two specific aims. Aim 1 will explore the significance of HIV-1 IN interactions with RNA for formation of the functional ribonuleoprotein complexes during the late stage viral replication. Aim 2 will characterize IN mutants that affect IN multimerization and/or IN- LEDGF/p75 binding. Mechanistic and structural details that will emerge from these studies will inform drug discovery efforts to develop improved ALLINIs for their clinical application.